The present invention is used in the field of automated analysis where liquids are pipetted with pipettes and fluids are stirred with stirrers as necessary.
The present invention provides a device for cleaning pipette probes or stirrers, comprising
a cavity that holds cleaning fluid and whose lower region has a fluid duct for filling and/or emptying the cavity, and
at least one inlet tube which empties into at least one nozzle directed toward the interior of the cavity.
When sample fluids such as blood or urine are analyzed, they must be pipetted into containers along with any necessary wash fluids, reagents, etc. The pipette must be rinsed between pipettings to avoid carryover between consecutive samples or reagents. If fluids must be mixed in automated analyzers, this is usually performed using stirrers that are lowered into the sample fluid. The stirrer must be cleaned between each step in the mixing procedure to avoid carryover of the material to be mixed by the stirrer. Examples of materials to be mixed include fluids and suspensions, such as magnetic microparticles in fluid.
Washing device for pipettes and stirrers are known from the prior art in which the devices to be washed are inserted into a cavity filled with wash fluid and the wash fluid is replaced after one or more wash steps. The fluid is usually replaced by removing the fluid through a fluid duct using suction.
A device for washing pipettes is described in European patent application 0 661 542 in which the pipette is inserted into a tube that surrounds the pipette at a distance of 1 mm or less. Fluid is injected into the tube to wash the pipette.
Devices with a cavity known in the prior art have the disadvantage in that the fluid is injected into and emptied from the cavity through the same fluid duct, making it inevitable that used and fresh wash fluid are mixed. Moreover, these devices have the disadvantage that they operate according to a dilution principle. In other words, the fluid that adheres to the pipette is diluted with the wash fluid. Even after the pipette is removed from the cavity, therefore, fluid which is contaminated to a certain extent is still adhered to it. Although this problem is avoided with the device described in EP-A-0 661 542, this device is limited to a certain type of pipette because the duct is designed to accommodate a pipette of a certain diameter. This wash device therefore cannot be used with different types of pipettes or for pipettes and stirrers interchangeably.
The task of the present invention was to provide a device for cleaning pipettes or stirrers very effectively that can be used to clean various objects such as different types of pipettes or stirrers. A further task of the invention was to provide a device with a simple mechanical design that can be integrated into existing automated analyzers or automated analyzer concepts.
A device for cleaning pipettes and stirrers provided by the invention has a cavity for holding cleaning fluid. The cavity is preferably shaped like a hollow cylinder with an internal diameter of between 0.7 and 3.5 cm. The cylinder can also have a base that is not round. The area of the cylinder that is filled with wash fluid is about 10 cm high, although it can vary up or down considerably, depending on the application. The cavity can be manufactured from a number of materials such as metals or plastics, with plastics being the preferred material. The device is preferably designed so that it can be securely attached to a base in an upright position. Moreover, the device has a number of openings.
The lower region of the cavity has an opening that serves as a fluid duct for filling and/or emptying the cavity. This opening is preferably located at the lowest point possible inside the cavity to ensure that used wash fluid can be removed from the cavity as completely as possible. This can be accomplished, for instance, if the bottom of the cavity is bent or slanted.
The upper region of the cavity has one or more openings for fluid ducts that empty into one or more nozzles. The one or more nozzles are directed toward the interior of the cavity and serve to spray a pipette probe or stirrer that is inserted into the cavity. Each of the nozzles is preferably positioned so that the fluid stream ejected from it points downward at a 20 to 70xc2x0xe2x80x94and preferably approximately 45xc2x0xe2x80x94angle from horizontal. If the device contains numerous nozzles, it is also advantageous for them to be positioned in such a way that the fluid streams meet at one point, preferably in the longitudinal axis of the cavity. In an especially preferred design, the nozzles are located in an insert that can be screwed into the cavity. A groove runs around the outside of the metal insert that contains holes for the nozzles. When the metal insert is screwed into the cavity, an intermediate space forms in the groove between the cavity and the insert that is filled with wash fluid through one or more inlet tubes. In an advantageous design, two inlet tubes are used that are positioned on opposite sides of the cavity. The insert that is screwed into the cavity can be manufactured from a number of materials such as plastics or metals. Metals are preferred, especially stainless steels such as 1.4435 and 1.4305 (old designations: V2A and V4A), that are resistant to cleaning fluids.
It is also advantageous to the function of the device provided by the invention if the upper region of the cavity contains at least one additional opening for another fluid duct, below the nozzles. The cavity can be filled with fresh wash fluid through this fluid duct. This fluid duct can also be used as an outlet for overflowing liquid or to empty fluids using suction to keep the column of water in the cavity at a defined level. This is especially advantageous if the fluid leaving the nozzles cannot be controlled exactly and the fluid level can therefore not be controlled simply by any other means. It is advantageous to know the fluid level in the cavity in advance to eliminate the need to perform liquid level detection, and to avoid inserting the pipette into the fluid farther than desired. This also makes it easier to standardize the wash processes.
The invention also provides a system consisting of a pipette probe attached to a drive arm or a stirrer attached to a drive arm, and a device for cleaning pipette probes or stirrers according to the invention. xe2x80x9cItem to be washedxe2x80x9d in the context of this application refers to both pipette probes and stirrers. Pipette probes or stirrers attached to a drive arm are commonplace in automated analyzers described in the prior art, so drive arms and their control mechanisms will not be described here in detail. For the present invention, however, it is important that a central control unit be provided that coordinates and regulates the movement of the drive arms and the control of the fluid streams and pumps. The drive arm must move the pipette probe or the stirrer over the opening in the cavity and lower the item to be washed into the cavity. The drive arm must therefore be capable of performing a rotational and translational movement in the vertical planes or translational movements in at least two spacial directions.
The invention also provides a method for cleaning pipette probes or stirrers using a device according to the invention in which the pipette probe or stirrer is inserted into the cavity and sprayed with wash fluid by at least one nozzle. It is favorable to lift the item to be washed to a height at which the area that is wetted with fluid during pipetting or stirring is located entirely below the level of the nozzles. On the other hand, it is unfavorable if an area of the item to be washed is sprayed that is larger than the one described above, because there is a risk of fluid being sprayed on electrical contacts or the like, or of decreasing the effectiveness of the washing procedure. It is especially favorable if the upper edge of the area of the item to be washed described above is located 5 to 5 mm below the level of the nozzle. It is advantageous for the spraying to take place while the item to be washed is lifted out of the cavity. The item to be washed can also be inserted into a wash fluid contained in the cavity. The purpose is to soften any deposits or caked-on substances from the item to be washed and remove them by spraying them with fluid from the nozzles. The item to be washed is cleaned with fresh wash fluid in the spraying step in order to prevent contaminating wash fluid from adhering to the surface of the item to be washed after the cleaning process is over. As a result, the wash station fills with this wash fluid. When cleaning pipette probes, it is also an advantage to rinse the inside of the probes in such a way that the probe is dipped into the wash fluid in the cavity and wash fluid is directed through it. Dipping the pipette probe into the wash fluid prevents the formation of an aerosol and even facilitates cleaning by causing fluid to swirl on the outside of the probe.
It is advantageous for the pipette probe to be dipped into the wash fluid in the cavity and removed at a speed of less than 14 cm/sec to ensure that all fluid covering the probe falls off without forming droplets. Once the pipette probe has left the fluid it can be moved at a higher rate of speed.
The processes for washing a pipette probe described above apply to both the inside and outside of the probe. It is also possible, of course, to wash just the inside or outside of the probe. It is especially advantageous to rinse the outside of the pipette between the individual uptake steps when drawing up two or more different fluids into the same pipette probe in order to prevent or at least reduce carryover. This is especially advantageous when analytical tests are performed with reagents that can also be detected as analytes. In a case like this, the reagent could be carried over from the first test into the sample and then lead to a false-positive test result in a subsequent test of this sample. When drawing up various fluids into one pipette probe, it has proven effective to draw up a separating fluid or a separating air bubble into the pipette probe after drawing up a fluid (e.g., reagent) and only then to draw up another fluid (e.g., reagent or sample).
Wash fluids (also called cleaning fluids) according to the invention refer to the fluids and mixtures commonly used with automated analyzers, e.g., aqueous solutions to which detergents, salts, preservatives, and possibly solubilizers have been added.